Thread anvils for inside micrometer

ABSTRACT

A thread gauge which attaches to an inside micrometer to measure the thread pitch diameter of internally threaded parts. A pair of anvils have external threads which match in pitch with the threads of the part. Each anvil has a bore which receives a ball and a slot which receives a stem projecting from the ball. Mounting sleeves connect the stems with the opposite ends of the micrometer. Each anvil can rotate on its ball about the stem axis so that the micrometer can be adjusted to position the anvils against the threaded part. The anvils can also move linearly on the balls to properly align with the threads of the part.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates generally to the measurement of thread pitchdiameters and more particularly to a gauge assembly for attachment to aninside micrometer to provide for the accurate measurement of the pitchdiameter of an internally threaded part.

When threaded parts are manufactured, it is necessary to accuratelymeasure the pitch diameter of the threads in order to assure that thepart has the necessary thread dimensions. Similarly, finished parts mustbe measured during inspection operations to check the pitch diameter.

The Government has rights in this invention pursuant to Contract No.DE-AC04-76DP00613 awarded by the U.S. Department of Energy.

In my co-pending application Ser. No. 568,837, filed on Jan. 6, 1984, Idisclose a thread gauge which can be used to measure the pitch diameterof both external and internal threads. However, the depth to which thegauge can be extended into an internally threaded part is limited by thelength of the blades of the caliper instrument to which the gauge isattached. Therefore, even though this device is entirely satisfactoryfor gauging inside threads on a fairly shallow lip of a part, it is notapplicable in situations where the internal threads are located on arecessed area of the part or where the threads are located too deeply inthe part to accommodate the caliper blades.

At present, parts which are internally threaded can be measured onlywith a thread plug gauge which is a go-no go device. The thread pluggauges have standard sizes and are thus able to measure only standardpitch diameters. The thread plug gauge is particularly unsatisfactory ifa large number of nonstandard threads are manufactured. In any case, thecost of maintaining a large number of different size plug gauges isoften prohibitive, since each gauge is useful only for a single size andis lacking both in versatility and adjustability.

Consequently, it is evident that a need exists for a thread gauge foraccurately measuring the thread pitch diameter of internally threadedparts. It is the primary goal of the present invention to meet thisneed.

More specifically, it is an object of the invention to provide a threadgauge which functions to accurately measure the thread pitch diameter ofinternally threaded parts having virtually any size and shape. In thisrespect, it is noteworthy that the thread gauge of the present inventioncan be applied to any part which can accommodate an inside micrometer,regardless of the location of the threads on the part.

In accordance with the invention, I provide thread anvils havingexternal threads which match the pitch of the internal threads that areto be measured. Each anvil is provided with a bore and a slot whichintersects with the bore. Each anvil has a spherical tooling ball whichfits closely in its bore. A stem projects from each ball and extendsthrough the slot in the anvil. This arrangement allows each anvil torotate on its ball so that the micrometer shaft can be turned while thethreads on the anvils remain properly oriented to mate with the internalthreads of the part which is undergoing measurement. At the same time,the slots permit the anvils to move linearly back and forth on the ballsso that the anvil threads can properly align with the threads of thepart.

The anvils can be attached to the opposite ends of virtually any insidemicrometer from the smallest size to the largest size. A mounting sleeveis fitted on each stem and secured thereto by a set screw. A second setscrew is used to lock each sleeve on the micrometer with each stempositioned end to end against the micrometer end. In this manner, theanvils are precisely located on the opposite ends of the micrometer sothat the known dimensions of the gauge can be added to the scale readingto thereby provide an accurate measurement of the pitch diameter of theinternally threaded part.

DETAILED DESCRIPTION OF THE INVENTION

In the accompany drawing which forms a part of the specification and isto be read in conjunction therewith and in which like reference numeralsare used to indicate like parts in the various views:

FIG. 1 is a perspective view showing an inside micrometer equipped witha thread gauge arrangement constructed according to a preferredembodiment of the present invention, with the thread anvils of the gaugeapplied to an internally threaded part to measure the thread pitchdiameter;

FIG. 2 is an exploded perspective view showing the components of eachthread gauge assembly, with a portion of the mounting sleeve broken awayfor purposes of illustration; and

FIG. 3 is a fragmentary sectional view on an enlarged scale takengenerally along line 3--3 of FIG. 1 in the direction of the arrows.

Referring now to the drawing in more detail and initially to FIG. 1, thepresent invention provides a thread gauge which is used with aconventional inside micrometer generally designated by numeral 10. Themicrometer 10 includes a thimble 12 having a thimble scale 12a thereonadjacent to a sleeve 14 having a vernier scale 14a. The thimble 12 isrotatable on sleeve 14 and extends and retracts when rotated to changethe overall length of the micrometer 10. The scales 12a and 14acooperate to provide a scale reading indicative of the overall length ofthe micrometer and thus the dimension of the part that is beingmeasured. The end of sleeve 14 opposite the thimble 12 connects with abarrel 16. Another sleeve 18 extends from barrel 16 to another barrel20. A rod 22 extends from barrel 20 and has a free end which forms oneend of the micrometer 10. The opposite end of the micrometer is formedby another short rod 24 (see FIG. 3.).

In accordance with the present invention, a thread gauge can be attachedto the inside micrometer 10 to measure the thread pitch diameters ofinternally threaded parts. The thread gauge includes a pair of metalanvils 26 which are identical to one another and mounted on the oppositeends of the micrometer 10. Each anvil 26 has a cylindrical outsidesurface which is provided with spiral threads 28. The pitch of threads28 is the same as the pitch of the threads on the internally threadedpart which is to be measured. Therefore, it is contemplated that anumber of different sets of anvils will be provided, with each sethaving threads with a different pitch so that parts with differentthread pitches can be measured.

The outside of each anvil 26 is machined to provide a flat surface 30which is unthreaded. A cylindrical bore 32 is formed through each anvil26 from end to end and is coaxial with the cylindrical exterior surfaceof the anvil. An elongated slot 34 extends into the flat surface 30 ofeach anvil and intersects with the bore 32. The length dimension of eachslot 34 is oriented parallel to the axis of the bore 32. The slots 34 donot extend the entire length of the anvils 26 but instead terminate inopposite ends 34a.

Each anvil 26 is provided with a tooling ball 36. Each tooling ball 36includes a spherical ball 38 and a cylindrical stem 40 which projectsfrom the ball 38. The balls 38 are substantially equal in diameter tothe diameter of the anvil bores 32. Each stem 40 is substantially equalin diameter to the width of the slot 34. Consequently, the stem 40 canbe extended into bore 32 and through slot 34 in order to position theball 38 in bore 32 with the stem projecting out of the anvil through theslot 34. The balls 38 fit closely in bores 32 but permit the anvils torotate on the balls. The stems 40 similarly have a close fit in slots 34but permit the anvils to slide linearly on balls 38 between limitingpositions defined when the stem 40 reaches the opposite ends 34a of theslot. Preferably, the balls 38 and anvils 26 are formed from hardenedtool steel to prevent them from wearing unduly.

A mounting sleeve 42 is used to attach each anvil 26 and tooling bar 36to the micrometer 10. Each sleeve 42 is cylindrical and is provided withthe central bore which includes a first bore portion 44a and a somewhatlarger bore portion 44b which forms a continuation of bore portion 44a.Bore portion 44a is substantially equal in diameter to stem 40, whilethe other bore portion 44b is substantially equal in diameter to therods 22 and 24 which form the opposite ends of the micrometer. A setscrew 46 is threaded into a passage which intersects with bore portion44a. Another set screw 48 is threaded into another passage whichintersects with bore portion 44b. Each mounting sleeve 42 has flat,annular opposite ends 42a and 42b.

In use, the thread gauge of the present invention cooperates with theinside micrometer 10 to measure the thread pitch diameters of internallythreaded parts such as the internally threaded ring 50. Spiral threads52 are formed internally on ring 50. The anvil threads 28 have the samepitch as the internal threads 52 on the ring.

The thread gauge is used by first applying the tooling balls 26 in themanner indicated previously. This results in the balls 38 being receivedin the anvil bores 32 with the stems 40 extending through slots 34. Themounting sleeves 42 are applied to the rods 22 and 24 which form theopposite ends of the micrometer. As shown in FIG. 3, sleeve 42 isapplied to rod 24 until the sleeve end 42b contacts the end of thethimble 12. Then, set screw 48 is tightened to secure the mountingsleeve on one end of the micrometer. The other mounting sleeve 42 issimilarly attached to the opposite end of the micrometer.

Next, the stems 40 are applied to the mounting collars 42 such that thestems extend through bore portions 44a into contact with the ends of themicrometer. This position is shown in FIG. 3, and it is noted that stem40 is located end to end with rod 24. Set screw 46 is then tightenedagainst stem 40 to thereby secure anvil 26 on the end of the micrometer.The length of each mounting sleeve 42 is such that the flat surface 30of anvil 26 is spaced slightly from end 42a of the mounting sleeve topresent a small gap between the anvil and sleeve. This gap is largeenough to permit each anvil 26 to freely rotate and move linearlywithout interference, and it is small enough to maintain the stabilityof anvils 26 on the ball elements 38.

After the anvils have been applied in this manner to the opposite endsof the micrometer 10, measurements can be taken of the pitch diameter ofan internal threaded part. The micrometer 10 is inserted into the ring50 and adjusted until the two anvils 26 are brought against the internalthreads 52 at diametrically opposed locations on the ring 50. Since theanvil threads 28 have the same pitch as the ring threads 52, the anvilthreads exactly mate with the threads on the ring, as shown in FIG. 3.The threads 28 fit closely in the grooves between threads 52, andthreads 52 similarly fit closely in the grooves presented between theanvil threads 28.

In order to apply the anvils to the internally threaded part, it isnecessary to turn the thimble 12. Since the anvils 26 are able to turnon balls 38, this can be accomplished while the anvils are maintained inthe proper orientations to mate with the threads 52 on ring 50. At thesame time, each anvil 26 is able to slide linearly on its ball 38 in thedirection of bore 32 or perpendicular to stem 30. This linear movementpermits the anvils to shift so that their threads can properly alignwith threads 52. The opposite ends 34a of slots 34 retain the anvils onthe tooling balls and limit the extent to which the anvils can slidelinearly. The slots are long enough to permit the anvil threads to alignwith the threads of the internally threaded part that is being measured.It is noted that end surface 42a of each mounting sleeve 42 confrontsthe adjacent flat surface 30 of the anvil 26. The interaction betweenthese two surfaces restricts anvils 26 to rotation on balls 38 about anaxis which is coincident with the axis of stem 40. Thus, the confrontingsurfaces of the anvils and sleeves maintain the stability of the anvilswithout restricting their freedom of movement as necessary to properlyengage with threads 52.

When micrometer 10 has been extended sufficiently to properly apply theanvils 26 to the internal threads 52, the pitch diameter of the partthat is undergoing measurement is equal to the measurement indicated onthe scales 12a and 14a, plus a number equal to the pitch diameter of theanvil threads 28 plus the diameter of ball 38 plus twice the length ofthe stem 40. Since the length of the stem 40, the diameter of ball 38and the pitch diameter of threads 28 are all known, the number whichmust be added to the scale reading is known and is the same for allparts that are undergoing measurement. Consequently, the measurement canbe easily carried out in all cases by adding a known number to themeasurement reading on the micrometer 10.

The thread gauge can be removed from the micrometer 10 simply byloosening set screws 48 and detaching the mounting sleeves 48 from theopposite ends of the micrometer. The micrometer can then be used in itsintended fashion for other measurements, or anvils having differentpitch diameters can be applied to it for use in measuring internallythreaded parts having different thread pitches. Set screw 46 can beloosened to detach the mounting sleeve 42 from the tooling ball 36, andthe tooling ball can be separated from anvil 26 if desired. If theanvils in each different anvil set have bores 32 and slots 34 of thesame size, the same tooling balls 36 and attachment collars 42 can beused to attach each set of anvils to the micrometer 10.

The thread gauge of the present invention can be used to measure insidepitch diameters on parts having virtually any size and configuration. Solong as the inside micrometer can be applied inside of the part and thelength of each anvil assembly can be accomodated, a measurement can betaken. The micrometer with the thread gauge attached can be inserted tovirtually any depth. At the same time, micrometers having virtually anylength can be used. For example, micrometers as short as one and onehalf inches can be used, as can micrometers as long as 40 inches andmore. The only requirement is that the anvils have threads with the samepitch as the threads of the part that is undergoing measurement.

The mounting arrangement for the anvils locates stems 40 end to end withthe micrometer and thereby precisely locates each anvil 26 at apredetermined location with respect to the micrometer end. This assuresthat each measurement will be accurate. Since the parts are preferablymade of hardened tool steel, wear is minimized and the accuracy ismaintained even after the thread gauge has been used extensively. Thethread gauge can measure the pitch diameter of virtually any type ofthread, including Acme threads, buttress threads and both English andmetric threads.

From the foregoing, it will be seen that this invention is one welladapted to attain all the ends and objects hereinabove set forthtogether with other advantages which are obvious and which are inherentto the structure.

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

Since many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

Having thus described the invention, I claim:
 1. A thread gauge forapplication to opposite ends of an inside micrometer to measure thethread pitch diameter of an internally threaded part, said thread gaugecomprising:a pair of anvils each presenting external threads havingsubstantially the same pitch as the threads of the internally threadedpart; a tooling ball for each anvil, each tooling ball including a ballelement and a stem extending from the ball element; means for mountingeach anvil on the corresponding tooling ball in a manner permitting theanvil to rotate on the ball element and move linearly on the ballelement in a direction generally perpendicular to the stem; and meansfor connecting said stems to the opposite ends of the micrometer tomount each anvil thereon at a predetermined location relative to thecorresponding end of the micrometer, whereby the micrometer can beadjusted to position the threads of the anvils against the threads ofthe internally threaded part at diametrically opposed locations thereonto provide a measurement of the pitch diameter of the internallythreaded part.
 2. The invention of claim 1, wherein said mounting meansincludes:a bore in each anvil closely receiving the ball element of thecorresponding tolling ball, said anvils being rotatable on the ballelements and being movable linearly thereon in the direction of the axesof the bores; and a slot in each anvil through which the stem of thecorresponding tooling ball extends, each slot having a length dimensionoriented parallel to the axis of the bore and a lesser width dimensionsubstantially equal to the diameter of the stem to permit the anvils tomove linearly on the ball element between limiting positions definedwhen the stem reaches opposite end of the slot.
 3. The invention ofclaim 2, wherein each anvil has an exterior configuration to present agenerally cylindrical surface on which said external threads are formedin a spiral arrangement and a substantially flat surface into which theslot extends, each bore being coaxial with the cylindrical surface ofthe anvil.
 4. The invention of claim 3, wherein said connecting meansincludes:a mounting sleeve for each stem having a first bore portion forclosely receiving the stem and a second bore portion for closelyreceiving one end of the micrometer; means for securing each sleeve tothe corresponding stem with the stem extending into said first boreportion of the sleeve; and means for detachably connecting said sleevesto the opposite ends of the micrometer with the micrometer endsextending into said second bore portions in end to end relation withsaid stems.
 5. The invention of claim 4, wherein each stem has a lengthto space said anvils away from said sleeves when the stems are end toend with the ends of the micrometer.
 6. The invention of claim 4,including an end surface on each sleeve located adjacent said flatsurface of the corresponding anvil to restrict each anvil to rotation onsaid ball element about an axis coincident with the axis of thecorresponding stem.
 7. The invention of claim 1, wherein said connectingmeans includes:a mounting sleeve for each stem having a first boreportion for closely receiving the stem and a second bore portion forclosely receiving one end of the micrometer; means for securing eachsleeve to the corresponding stem with the stem extending into said firstbore portion of the sleeve; and means for detachably connecting saidsleeves to the opposite ends of the micrometer with the micrometer endsextending into said second bore portions in end to end relation withsaid stems.
 8. The invention of claim 7, including flat surfaces on eachanvil and sleeve confronting one another to limit each anvil to rotationon its ball element about an axis coincident with the axis of thecorresponding stem.
 9. The invention of claim 7, wherein said securingmeans includes a set screw threaded into each sleeve and engaging thecorresponding stem to secure the sleeve on the stem.
 10. The inventionof claim 7, wherein said detachable connecting means includes a setscrew threaded into each sleeve and engageable with one end of themicrometer to secure the sleeve on the micrometer end.
 11. Incombination with an inside micrometer having opposite ends, a threadgauge arrangement for measuring the thread pitch diameter of aninternally threaded part, comprising:a pair of anvils each having agenerally cylindrical exterior surface provided with spiral threadshaving the same pitch as the threads of the threaded part, said anvilsbeing applicable to the threaded parts at diametrically opposedlocations thereon with the threads of the anvils mating with the threadsof the threaded part; a bore extending in each anvil axially therein; aslot in each anvil connecting with the bore thereof; a ball elementreceived closely in the bore of each anvil, said anvils being rotatableon the ball elements and being movable linearly thereon; a stemextending from each ball element through the slot of the correspondinganvil, said anvils being movable linearly relative to said stems withsaid slots limiting the linear movement of the anvils and maintainingthe anvils on the ball elements; and means for detachably connectingsaid stems to the respective opposite ends of the micrometer to mountsaid anvils thereon at predetermined locations, whereby the micrometercan be adjusted to engage the anvils against the internally threadedpart with said slots accommodating linear movement of the anvils on theball elements to permit the threads of the anvils to mate with thethreads of the internally threaded part.
 12. The invention of claim 11,wherein each slot has opposite ends against which the stem is engageableto define limiting positions for the linear movement of each anvil onthe ball element.
 13. The invention of claim 11, wherein:each stem has afree end; and said detachable connecting means is operable to connectsaid stems in end to end contact with the opposite ends of themicrometer.
 14. The invention of claim 13, wherein said detachableconnecting means includes:a mounting sleeve for each stem having a firstbore portion for closely receiving the stem and a second bore portionfor closely receiving one end of the micrometer; means for securing eachsleeve to the corresponding stem with the stem extending into said firstbore portion of the sleeve; and means for detachably connecting saidsleeves to the opposite ends of the micrometer with the micrometer endsextending into said second bore portions in end to end relation withsaid stems.
 15. The invention of claim 14, including confrontingsurfaces on said sleeves and anvils cooperating to limit each anvil torotation on its ball element about an axis coincident with the axis ofthe corresponding stem.
 16. A thread gauge for use with an insidemicrometer having opposite ends to measure the thread pitch diameter ofan internally threaded part, said thread gauge comprising:a pair ofanvils each having an exterior configuration presenting a generallycylindrical surface provided with spiral threads and a substantiallyflat surface, said threads having the same pitch diameter as the threadsof the internally threaded part; a cylindrical bore extending througheach anvil, said bores being coaxial with said cylindrical surfaces; aslot in each anvil extending into the flat surface thereof andconnecting with said bore, each slot having a length dimension orientedparallel to the axis of the bore and a width dimension transverse to thelength dimension; a ball element fitting closely in the bore of eachanvil with the anvils being rotatable on the ball elements and movablelinearly thereon in the direction of the bore axis; a stem extendingfrom each ball element through the slot of the corresponding anvil, eachstem having a free end projecting beyond the flat surface of the anviland each stem having a diameter to fit closely through the slot topermit the anvils to move linearly on the ball elements with limitingpositions defined when the stems reach opposite ends of the slots; amounting sleeve for each anvil, each sleeve having a first bore portionfor closely receiving the corresponding stem and a second bore portionfor closely receiving one end of the micrometer; means for securing saidsleeves to said stems with the stems extending into said first boreportions; and detachable means for connecting said sleeves to theopposite ends of the micrometer with the micrometer ends extending intosaid second bore portions in end to end relation with said stems,thereby mounting said anvils at predetermined locations on the oppositeends of the micrometer to permit the micrometer to be adjusted toposition the anvils against the internally threaded part atdiametrically opposed locations thereon for measurement of the pitchdiameter of the part.
 17. The invention of claim 16, including an endsurface of each sleeve confronting said flat surface of thecorresponding anvil to restrict each anvil to rotation on its ballelement about an axis coincident with the axis of the correspondingstem.
 18. The invention of claim 17, wherein the end surface of eachsleeve is spaced from the flat surface of the corresponding anvil. 19.The invention of claim 16, wherein said securing means includes a setscrew threaded into each sleeve and engageable with the correspondingstem.
 20. The invention of claim 16, wherein said detachable meansincludes a set screw threaded into each sleeve and engageable with oneend of the micrometer to connect the sleeve thereto.